500 POPULAR SCIENCE MONTHLY. 



over nation. Glancing backward, however, over that long and varied 

 line of animal life shown to us in fossil forms — their history incon- 

 testably preserved for us direct from the hand of creation, we must 

 readjust our vision, enlarge our horizon to grasp the significance of the 

 origin, distribution, adaptation and survival of life. Life is here — 

 life has been a feature of this old earth's history through countless 

 ages. Whence came it, what have been the paths it has followed in 

 its development and adaptation to the varied conditions of earth, sea, 

 land and air? It would be presumption too gross to admit of tolera- 

 tion to assume to fully discuss so extensive a problem within the lim- 

 its of a magazine article, but an effort will be made to point out in a 

 rapid survey some of the factors that seem to have been effective in 

 the peopling of the earth. 



First, we should observe the conditions that have existed and that 

 had to be met in the growth of organic beings — for we should not for- 

 get that life has had to adjust itself to conditions that existed prior 

 to its appearance, since the conditions have not been modified to accom- 

 modate its needs. 



Stretches of water and great reaches of land and the atmosphere 

 furnish the basis upon which organisms must act, and either water or 

 air, the medium that must serve them for many of their most vital func- 

 tions. Glancing over the opportunities for survival of life in a deli- 

 cate, simple condition, we can hardly fail to recognize the water as the 

 most natural element for primal life-forms. Indeed, I think no nat- 

 uralist will hesitate to consider water or, at least, an extremely moist 

 location as the necessary condition for the beginning of life. More- 

 over, any serious consideration of the question must force the convic- 

 tion that life-forms in other less favorable locations must have reached 

 such location by gradual modification and adaptation. For instance, 

 we can hardly conceive of the peopling of an arid desert-region with 

 forms such as lizards, snakes, horned toads, scorpions, beetles, etc., 

 except by the gradual encroachment upon desert area from adjacent 

 territory by animals which were able to adapt themselves to desert con- 

 ditions. Or, to put it in another form, the change to desert conditions 

 in previously watered area must be accompanied by the driving out or 

 extinction of all animals unable to adjust theruselves to the new condi- 

 tions. Assuming, then, a primary aquatic habitat for animal life, it 

 becomes of interest to inquire both as to the most probable point of 

 origin and as to the direction of adaptations. 



While some naturalists argue for a pelagic origin of the simplest 

 organisms, others hold to the idea of an origin near the shore, but in 

 either case we have evident lines of travel from siich a point to occupy 

 the surrounding space. Thus from a near shore location life might 

 work itself shoreward, adapting itself to the variable conditions of ebb 



